1. Field of the Invention
This invention relates to the alkylation of isoparaffins with olefins to yield hydrocarbons of enhanced octane number, the apparatus, catalyst and the method of preparing the catalyst.
2. Related Art
Isooctanes or trimethylpentanes (TMP) are among the most desirable components of motor alkylate gasoline and 2,2,4-trimethylpentane (isooctane) has long been the standard of measurement for the anti-knock properties of gasoline. The most common method of producing motor alkylate isooctane in commercial refineries is the alkylation of isobutane with butenes in the presence of a strong acid catalyst. Two acids currently used in alkylation plants are concentrated sulfuric acid and hydrofluoric acid. In these common processes the reactants are admixed with the acid in a contactor and the products separated from any unreacted reactants and the acid. The prior art in this area is well known. The drawbacks to the use of the sulfuric or hydrofluoric acid processes are readily apparent. Large quantities of the acids, which are highly corrosive, dangerous to handle and potentially a hazard to the environment, are required.
The search for safer particulate solid catalysts has been intense. Zeolites have been the most widely studied of the solid alkylation catalysts. For example, Kirsch, et al in U.S. Pat. Nos. 3,665,813 and 3,706,814 disclose the use of such zeolites in "continuous" alkylation processes. European Patent 0174863 discloses sulfated zirconia as a solid superacid for paraffin isomerization and isoparaffin alkylation. U.S. Pat. Nos. 4,056,578 and 4,180,695 disclose perfluoropolymersulfonic acid (PFPSA) as an alkylation catalyst U K. patent 1,389,237 discloses an antimony pentafluoride/acid on a carbon support as catalyst for alkylation. Other catalyst compositions which have been found to be initially active for alkylation include supported HF-antimony pentafluoride, (U.S. Pat. No. 3,852,371); a Lewis Acid and Group VIII metal intercalated in graphite, (U.S. Pat. No. 3,976,714); and a cation exchange resin complexed with BF.sub.3 and HF (U.S. Pat. No. 3,879,489). U.S. Pat. No. 4,918,255 describes a process for alkylating isoalkanes with olefins using a Lewis acid such as boron trifluoride, boron trichloride, antimony pentafluoride or aluminum trichloride deposited on inorganic oxide such as a wide pore zeolite, SiO.sub.2 or Al.sub.2 O.sub.3 .
Early work by Kirsch, et al, cited above using zeolites disclosed a catalyst life of about 10 grams of alkylate per gram of catalyst used. Further a method for increasing the life of zeolite catalysts using a regenerative process disclosed as in U.S. Pat. Nos. 3,851,004 and 3,893,942 issued to Chang-Lee Yang, which disclose incorporating a Group VIII metal hydrogenation agent into the catalyst composition and regenerating the partially deactivated catalyst by periodic hydrogenation. A similar catalyst was used by Zabransky, et al, in a simulated moving bed reactor as disclosed in U.S. Pat. No. 4,008,291.
Fenske et al. in U.S. Pat. No. 3,917,738 claims both oxidative and reductive regeneration techniques for zeolite catalysts. As described in this patent the olefins are adsorbed by the catalyst. A mixture of catalyst, isoalkane and olefin flows concurrently through an adsorption zone before the reactants and catalyst are introduced into the reaction zone. The controlled olefin adsorption was thought to prevent polymerization and improve catalyst life although this benefit was not quantified.
It is an advantage of the process of the present invention that the catalyst life is extended over that described in the art for solid paraffin alkylation catalysts. It is a feature of the present invention that the catalyst environment is controlled in a circulating bed reactor. It is a further feature of the present invention that the catalyst contact with olefin rich streams is minimized and contact with isoalkane is maximized. It is a further advantage of the present invention that back-mixing of the flow stream is limited. A further feature of the present invention is a catalyst which has the appropriate alkylation activity and fluidization properties for use in this process. These and other advantages and features will be seen in the following description.